The Cahill family is a fictional family featured in the popular book series called The 39 Clues. They are known for their intelligence, resourcefulness, and adventurous spirit. The family is deeply involved in a global treasure hunt that spans various countries and historical events, making them central characters in the series. The Cahills are divided into several branches, each with unique traits and skills. The most notable branches include the Lucian, Ekaterina, Janus, and Thomas families. Throughout the series, members of the Cahill family work together and face challenges, uncovering secrets about their ancestry and the powerful Cahill legacy.